Body bias refers to the application of a non-zero voltage between the body and source terminals of a transistor. Since these terminals form a p-n junction, a voltage that forward biases the p-n junction is said to apply a forward body bias to the transistor. Similarly, a reverse body bias may be applied to the transistor by reverse biasing the p-n junction. Generally, body bias may be used to modulate the threshold voltage of a transistor to provide increased performance or reduced power consumption. A forward body bias may be used to increase an operational frequency of a transistor during an active mode, while a reverse (or zero) body bias may be used to reduce leakage currents during a standby mode.
Body bias may be controlled by controlling a bias voltage that is applied to a transistor body. A body bias generator typically regulates this bias voltage. A conventional body bias generator is suitable for regulating the bias voltage in a case that current flows in a single direction (i.e., in or out) with respect to the transistor body. Since a direction of current within a transistor body may differ based on whether a forward or reverse (or zero) body bias is applied to the transistor, a conventional body bias generator may be unsuitable for systems in which forward body bias or reverse body bias may be selectively applied.